1. Field of Technology
The present invention relates to an all-solid-state battery having a high output power and a long life, exhibiting high safety, and being produced at a low cost.
2. Description of Related Art
In recent years, demand for batteries has significantly expanded along with development of portable equipment such as a personal computer, cellular phone, and the like. As the medium used in order to move ions in the batteries in these applications, liquid electrolytes (electrolytic solutions) such as an organic solvent have conventionally been used. Batteries in which such an electrolytic solution is used may have a risk of leakage of electrolytic solution and the like.
In order to solve such a problem, development of an all-solid-state battery in which a solid electrolyte is used instead of a liquid electrolyte and all other components are formed from solid materials has been undertaken. Such an all-solid-state battery not only has no risk of liquid leakage due to the use of a solid electrolyte, but also is free of problems such as deterioration of battery performance caused by corrosion and the like. In particular, an all-solid lithium secondary battery is a popular target of development among researches in various fields as a secondary battery of which the energy density can be easily increased.
As a related prior art, a lithium secondary battery in which a conductive lithium ion electrolyte such as Li2S—SiS2—Li3PO4, etc. is used as a solid electrolyte has been disclosed (e.g. JP-A-5-205741).
However, the all-solid-state battery using a solid electrolyte as the electrolyte can output less energy than batteries using a liquid electrolyte. It has been difficult to draw a large current from the all-solid-state battery. Other problems with the all-solid-state battery are poor rate characteristics and cycle characteristics during charging and discharging and a short battery life as compared with batteries using a liquid electrolyte.
In order to solve these problems, a solid electrolyte battery in which the same inorganic oxide material as the solid electrolyte is interposed between electrode active material particles to increase the electric current that can be drawn and to improve charge-and-discharge cycle characteristics has been disclosed (e.g. JP-A-2000-311710).
However, the solid electrolyte battery disclosed in JP-A-2000-311710 has still to be improved in the output characteristics and charge-and-discharge cycle characteristics. Therefore, development of an all-solid-state battery exhibiting a higher output and having a longer life is demanded from the industrial world.
The present invention has been achieved in view of these problems in prior art and has an object of providing an all-solid-state battery having a high output power and a long life, exhibiting high safety, and being produced at a low cost.
As a result of extensive studies to attain the above object, the inventors of the present invention have discovered that the cause of difficulty in increasing delivery of a large current and improving charge-and-discharge cycle characteristics is low ion conductivity of a solid electrolyte. The inventors have further found that the above object can be achieved by using a cathode active material, an anode active material, and a solid electrolyte shown respectively by the later-described formulas (1) to (3). This finding has led to the completion of the present invention.